CP1300 Networks

Networks

• Transmitting information
  • Phone calls (one to one or conference)
  • FAX (one to one)
  • Computers (one to one at high level, one to many at low level)
  • Radio (one to many)
  • TV (one to many)

• Medium of transmission
  • Wire-based
    • Phone lines (56Kbits per second, long distance connections)
    • Twisted-pair cables (1MByte per second, close range connections)
    • Coaxial cables (20MBytes per second, connections within 1Km)
    • Fiber-optic cables (GBytes per second, long distance connections)
  • Wireless broadcast
    • RF (no line of sight)
    • Microwave (line of sight)
    • Satellite (line of sight)
  • Digital and Analog
    • Analog - continuous signal
    • Digital - discrete signal
    • Many media are analog, computers are digital
    • To send digital on analog media requires an analog to digital converter, e.g., a modem

• Network Models
  • Peer-to-Peer
    • All computers are equal in power
    • Running the network is shared by all computers
    • Resources are spread through all computers
  • Client-Server
    • A small number server computers provide shared access for many client computers
    • Server computers are specialized, high performance machines
    • Servers store: shared applications, data, system files
    • Clients are typically a lot less powerful than the servers
    • Clients make requests to the servers to access resources e.g., programs, data files, printers
  • Packet Switched
    • Data is transmitted in packets
    • Packet = data + destination information (e.g. IP address)
    • The packet is sent from one machine to the next until the destination machine is reached
    • Routers coordinate the network load and transmissions of packets

• Types of Networks
  • Local Area Networks (LAN)
    • Small range networks, buildings close together
    • 10s to 100s of machines
    • Client-Server and Peer-to-Peer communication
  • Wide Area Networks (WAN)
    • Distributed networks, not restricted to one location
    • >1000s machines
    • Packet switched communication
  • Building a network
    • Network cards
    • Transmission medium
    • Bridges to connect similar LANs
    • Gateways to connect different types of LANs

• The Internet
  • Physical
    • Each machine has a 32 bit IP number, e.g., 137.219.47.69
    • IP number has 4 octets, in two parts: network and machine
    • 1st octet 1-127
      • Class A network
      • Network number in 1st octet, machine number in others
      • 127 networks
      • 16M machines
    • 1st octet 128-191
      • Class B network
      • Network number in 1st and 2nd octet, machine number in others
      • ~16K networks
      • 64K machines
    • 1st octet 192-223
      • Class C network
      • Network number in 1st to 3rd octet, machine number in last
      • ~2M networks
      • 255 machines
    • 1st octet 244 onward
      • Multicast network
  • Logical
    • Hierarchy of domains
    • Names are resolved to IP numbers
    • Routers and gateways forward packets to the required IP address
  • Protocols
    • Network level
      • IP - Smallest data level. Unreliable and unordered
      • RIP - For sharing routing data
      • ARP - For resolving names to addresses
    • Transport level
      • UDP - On IP to make it reliable
      • TCP - On IP to make it reliable and ordered

Self assessments

• Networks

Tutorial Questions

• Networks (Answers)

Exam style questions

1. What are the ways information can be transmitted?
2. How are LANs connected together?
3. What do ADC and DAC stand for?
4. What is the packet-switching system for WANs?